Abstract:The construction machines, such as the crane, hydraulic grab and etc., utilize the hydraulic lifting system. The conventional hydraulic lifting system usually can not recover the potential energy of the heavy object. In order to avoid the object falling too fast, a throttle valve is set in the oil circuit to limit the falling velocity of the object. Therefore, the potential energy will be converted into the thermal energy, which not only brings the energy loss and also could cause some thermal problems. In order to avoid the loss of energy, an energy-saving composite cylinder hydraulic lifting system is designed. This paper presents the basic structure and working theory of this new hydraulic lifting system. By utilizing composite cylinder with special structure combined with accumulator, this system can limit the lowering velocity of heavy object and also could recover the potential energy of the object being lowered. Thus, this system has remarkable effect of energy-saving. The parameters of the accumulator used in this system are determined. The mathematical model of lifting condition is proposed, and the simulation analysis of lifting condition is conducted as well.